This invention concerns an improvement in the fabrication of transparent polarizing laminated glasses and the glasses obtained by this method.
U.S. application Ser. No. 446,551, filed Dec. 3, 1982 (based upon French Patent Application No. 8213076, published as No. 2,531,235), describes a transparent polarizing laminated glass comprised of:
(a) an inorganic or organic glass substrate;
(b) a coating with polarizing properties deposited on one of the surfaces of the substrate; and
(c) a unitary composite film that is optically transparent which consists of a ply of thermoplastic polyurethane having adhesive properties and a ply of thermosetting polyurethane with tear resistant and self-regenerating properties, the thermoplastic polyurethane ply adhering to the coating having polarizing properties.
The substrate can be, among others, a glass with photochromic properties.
The polarizing coating can be formed of a mixture of three organic colorants corresponding to the three primary colors blue, red, and yellow and exhibiting a nematic state, said polarizing coating having a reduced water solubility as a result of an ion exchange treatment by an aqueous acid solution of inorganic salts.
In the composite film the thermoplastic polyurethane is formed from an aliphatic diisocyanate and a diol of an aliphatic diacidic polyester or a diol of a polyglycol ether, each one of said diols having a molecular weight of 500-4000, and the thermosetting polyurethane is the product of (a) a polyglycol ether resulting from the combination of 1,2-epoxypropane with 2,2-bis(hydroxymethyl)1-butanol and containing 10.5-12% by weight of free hydroxyls, and (b) a biuret of 1,6-hexamethylene diisocyanate containing 21-22% by weight of isocyanate groups, the weight of said biuret being 0.9-1.1 times the weight of said polyglycol ether, the thermoplastic polyurethane ply ranging from 0.01-0.8 mm and the thermosetting polyurethane ply ranging from 0.2-0.8 mm.
If desired, the composite film may be subjected to a coloring treatment.
In the above-mentioned patent application there is also described a process for fabricating this transparent polarizing laminated glass which comprehends the following steps:
(a) forming parallel microgrooves on the inorganic or organic substrate which is to receive the polarizing coating by means of a very slightly abrasive brushing of said substrate;
(b) carefully washing the surface of the substrate that is to receive the polarizing coating and drying this surface;
(c) depositing on the washed and dried surface of the substrate a mixture of three organic colorants corresponding to the three primary colors and exhibiting a nematic state;
(d) treating the resulting polarizing coating by immersing in an aqueous solution of inorganic salts having an acid pH in order to reduce the water solubility of said polarizing coating; and
(e) applying the composite polyurethane film by first subjecting it to conditions of moderate temperature and pressure in order to insure a gradual and crease-free spreading out and adherence of the film to the polarizing coating, and then to conditions of high temperature and pressure in order to reinforce the mechanical bond between the film and the coating and to achieve cross linking of the composite film.
In certain applications, particularly when the laminated glass is a glass blank for eyeglasses which is subjected to an operation known as "edging" (finishing of the outside in order to form the glass to the shape of the frame in which it is to be mounted), it is advisable to carry out an additional step consisting of applying, after drying, a resin polymerizable by ultraviolet radiation to the cross section of the laminated glass, thereafter exposing the resin layer to ultraviolet rays to cause the resin to harden, this being done in order to prevent moisture from infiltrating into the laminated glass and to bring about in the end the destruction of the polarizing layer by delamination, particularly at the polarizing coating-glass substrate interface, since the edging operation, in effect, has the disadvantage of breaking through the thin stabilizing layer formed on the polarizing coating at the level of the cross section of the glass.
The above-discussed previous process has certain deficiencies:
The level of adhesion between the polarizing coating and the glass substrate is relatively weak such as to produce, during edging, separations that involve the rejection of a rather high percentage of edged laminated glasses and, therefore, increased cost.
The layer of polymerizable resin applied to the cross section of the laminated glass after edging imparts, after polymerization, only a mediocre aesthetic appearance to the finished laminated glass. In addition, the operation of applying this layer of resin is rather tedious and adds to the complexity of the former process.
Therefore, it would be very advantageous to devise an improved process to permit simplification of the entire fabrication process, to reduce the cost of fabrication, and to improve the reliability of the final product.